Device for indicating abnormal operating conditions in electrode furnaces



Aug. 13, 1968 E. HELSING ET AL 3,397,277 DEVICE FOR INDICATING ABNORMALOPERATING CONDITIONS IN ELECTRODE FURNACES Original Filed Sept. 13, 19652 Sheets-Sheet l Fig.

INVENTORS 1PM'%4 5/4 6 A04 s'- 4-7914. 57/90/27 Aug. 13, 1 968 E.HELSING ET AL DEVICE FOP. INDICATING ABNORMAL OPERATING CONDITIONS INELECTRODE FURNACES Original Filed Sept. 15, 1965 2 Sheets-Sheet 2 m w Jm M M W 3 M Na M K United States Patent DEVICE FOR INDICATING ABNORMALOPERAT- ING CONDITIONS IN ELECTRODE FURNACES Erik- Helsing and Nils-ErikStrorn, Vasteras, Sweden, as-

- signors to Allmanna Svenska Elektriska Aktiebolaget,

Vasteras, Sweden, a corporation of Sweden Continuation of applicationSer. No. 486,972, Sept. 13, 1965. This application Nov. 1, 1966, Ser.No. 591,337 Claims priority, application Sweden, Mar. 2, 1962, 2,311/ 622 Claims. (Cl. 1313) ABSTRACT OF THE DISCLOSURE In an arc furnace havinga motor for adjusting the position of anelectrode, a variable magnitudeof the furnace is measured and compared with a reference magnitude. Anamplifier emits signals when there is a difference between the referencesignal and the measured signal. Time delay means connect the amplifierwith the control means for the motor. A continuous output signal isfurnished from the amplifier when the measured value is either greateror less than the reference value, and the time delay means are startedin response to either of such conditions, and act to stop the motorafter a predetermined time if such signals continue.

The application is a continuation of application Ser. No. 486,972, filedSept. 13, 1965, which in turn is a continuation-in-part of applicationSer. No. 262,706, filed Mar. 4, 1963, both of said applications beingnow abandoned.

I The invention relates to a device for use in the regulation ofelectrode furnaces, such as reduction furnaces, by means of electrodemovement in accordance with certain measured values, such as current,impedance or resistance. In certain types of reduction furnaces abnormaloperating conditions sometimes arise which cause a substantial change ofthe resistance. With automatic regulation to ensure constant current,impedance or resistance, a. considerable regulation is obtained undersuch operatin-gconditions, with changing of the electrode positioninorder to maintain the regulated magnitude constant. This is generallynot desirable for two reasons. Partly an unnecessary electrode movementmay worsen the condition, partly the abnormal operating condition canoften only be eliminated by metallurgical means. A problem is thus toprevent such long-running electrode movement without for that reasongiving up the advantages of electrode regulation.

An example of furnaces where such operating problems may arise iselectric flowing furnaces, where socalled slag boiling may arise,causing a substantial raising of the resistance and lowered electrodecurrent. With automatic electrode regulation a considerable downwardmovement of the electrode is obtained in this case, a phenomenon whichit is desirable to avoid for the reasonthat such a downward movementgenerally worsens said abnornal operating condition, which can only beeliminated by metallurgical means.

The invention is aimed at a solution of these and other rather similarproblems in connection with electrode furnaces and is characterised inthat the duration or amount of each electrode movement is arranged to bemeasured by means of a measuring means which is arranged to give asignal after a certain measuring value for each electrode movement whichvalue is preferably adjustable. Said signal may block an automaticelectrode regulating device and possibly also disconnect the adjustingmotor of the electrode. Although the abnormal phenomena make themselvesknown by longer duration or 3,397,277 Patented Aug. 13, 1968 amount ofeach electrode movement it is in this way possible to obtain a signal,which calls the attention of the furnace attendant to the situation.Thereby necessary metallurgical or other measures may be carried out ingood time. It is also possible upon such a signal automatically ormanually to stop the electrode movement.

The invention is illustrated in the accompanying figures, of whichFIGURE 1 shows a diagram, electrode speed-time under normal operatingconditions. FIGURE 2 shows the same under abnormal operating conditions,partly without and partly with the use of the invention. FIGURE 3 showsa blocking circuit for electrode regulation according to the invention.FIGURE 4 shows the circuit of FIGURE 3 in more detail.

In FIGURE 1 is shown the electrode movement (in mm./s.) under a normalregulating process. Blocks directed upwards represent electrode raising,those directed downwards electrode lowering. With the normal furnaceoperation shown in FIGURE 1 the movements may in no event have anextension in time exceeding a certain definite time. In this case theduration (in seconds) of each electrode movement is measured, but onecan also measure the movement (or integrate the speed of movement), forexample with variable speeds of movement. Following a diagram accordingto FIGURE 1 a certain suitable maximum value may be defined which in allcases exceeds the connection times occurring in FIGURE 1 (normaloperating conditions).

In FIGURE 2 is shown an abnormal regulating process partly without (tothe left of the dotted line 11) and partly with a connected measuringand regulating device according to the invention. An abnormalphenomenon, for example slag boiling in a flowing furnace, makes itselfknown as a regulating movement with longer duration (and/ or longermovement). To the right of the line 11 is shown a measuring of theduration of an electrode movement (see 12), and after a certain set time(T) or movement (mm/s.) a signal is given (acoustic or optical) andpossibly a regulating signal may also issue from the measuring means(not shown in FIGURES 1 and 2) to another means for stopping theelectrode movement, for example blocking of the electrode regulation orbreaking of the current supply to the electrode adjusting motor. Thissignal may of course be amplified in a suitbale way. After such a signalthe furnace attendant may put into effect necessary measures in thefurnace for improving the abnormal condition. The device may bemultiplied for an electrode furnace, for example one per electrode, oralso a common device may be used for the whole furnace. Several signalmeans per electrode may also be used, for example, one pre-warningsignal, one action signal and an extra warning signal.

A simplified block scheme for a device according to the invention isshown in FIGURE 3. At 13 a reference value is fed in which is comparedwith the measuring value for the regulating magnitude, such as current,re-

sistance, impedance. The out-signal of this is fed to an amplifier 14,which in its turn feeds an auxiliary member 15, such as an auxiliaryrelay, which in its turn operates the adjusting motor 17 of theelectrode 19. According to the invention the auxiliary member 15 alsooperates a time means 16, such as a time relay, which, after a certainset value is reached, is arranged to block the regulating circuit atdifferent places, for example according to the drawing at 17. Thecircuit is re-connected at 18 and in a suitable way adjusts the timerelay 16 to zero after the completion of each electrode movement. Therunning time of the time relay is thus compared with the running time ofthe electrode.

The regulating circuit of FIGURE 3 is shown in more detail in FIGURE 4.An arc furnace 19, 20 with electrodes 19, for example a three-phasefurnace with three electrodes 19, each of which is adjusted by anelectrode adjusting motor 17 (see also FIGURE 3) is shown (one phase) inFIGURE 4. Some value in said furnace (one phase of Which is shown inFIGURE 4) is measured, here furnace current I, and a signal proportionalto said value is fed over a current transformer 21 and impedances 22 and23 to the input side of each of two amplifiers 24, 14 (see FIGURE 3).The signal to amplifier 24 is fed over amplitude limiters 25 of awell-known type to the amplifier 24, which is of the integrating type,here accomplished by means of a shunted capacitor 27 and impedance '26.The integrated amplified output signal from amplifier 24 is over a relaycoil 28 and a sampling device 29 coupled to the electrode adjustingmotor 17. The relay coil 28 belongs to a maximal relay, the contact 30of which is series-coupled with the motor 17, and when said outputsignal exceeds a certain maximal value, the motor 17 is uncoupled. Theamplifier 24 with auxiliary devices, including the sampling device 29 isdescribed in application Ser. No. 262,707 (now abandoned), filed Mar. 4,1963.

A value corresponding to the furnace current I is fed over impedance 23and conductors 31 to the input side of amplifier 14. Said value iscompared with an adjustable reference value (from conductors 32 andpotentiometer 33) and the difference value of said two input signals isfed to the input side of amplifier 14. The amplifier 14 (and 24) may beof a kind well-known in the art. The output side of the amplifier 14 isfed to a network consisting of two parallel coupled, oppositely directedrectifiers 34, 35, each series coupled with a relay coil 36, 37respectively. Each of said coils co-operates with a contact (only one,38, being shown) in a time circuit for a relay coil 39, thecorresponding contact 41 of which is series coupled with a coil 40 of atime relay. Said relay has two contacts 42, 43, one series-coupled witha signal lamp 44 to a DC source, one series-coupled in the feed circuitof motor 17. (Parts 39-43 correspond to part 16 of FIGURE 3.) Thecontrol circuit of the amplifier is fed back (at 45) from the feedcircuit (at 46) of motor 17 or elsewhere.

The device in accordance with FIGURE 4 acts in the following manner:When a current error occurs, the electrode motor 17 and electrode 19 areregulated by amplifier 24 as described in application Ser. No. 262,707(now abandoned). The error signal is fed over 31 to the input side ofamplifier 14, the output signal of which is fed over rectifiers 34, 35,to the coils 36, 37, depending on whether the error is or A certainerror signal actuates coil 37 and thus contact 38 is closed, and after adelay (see the delay circuit with capacitor 47 at contact 39) contact 41is also closed by coil 39. The time delay is dependent on the values ofcapacitance 47 and the other members in said circuit. After the closingof contact 41 the lamp circuit(42, 44) is closed and (possibly) themotor circuit is opened at 43.

If said error signal disappears before the time delay of coil 38 plusthe time delay of circuit 39-47, contact 38 is reopened and after awhile also contact 41, and the lamp 44 is not lit and contact 43 is keptclosed.

If the error signal last longer, lamp 44 is lit and (possibly) motor 17is stopped by means of the opening contact 43.

The object of the invention may be used at the same time with otherelectrode regulating devices and may in a suitable way be on-and-offconnected. The range of 4 application is not limited to certain types ofelectrode furnaces but may be used with all types, where extra longduration or amount of an electrode movement may involve drawbacks andsignify an operating condition which demands special measures, which thenormal regulating equipment is not capable of carrying out.

While we have described herein one embodiment of our invention, we wishit to be understood that we do not intend to limit ourselves therebyexcept within the scope of the claims hereto or hereinafter appended.

We claim:

1. Automatic control means for an arc furnace comprising means formeasuring a variable magnitude of the furnace, an adjusting motor for atleast one of the electrodes, control means for said motor, an amplifier,a reference magnitude supply means, means connecting said referencemeans and said measuring means to said amplifier, said amplifieremitting signals depending on the difference between the output signalsfrom said reference and said measuring means, time-delay meansconnecting said amplifier with said motor control means and includingmeans to furnish a continuous output signal from said amplifier when themeasured value is greater than the reference value and means to supply acontinuous output signal from said amplifier when the measured value issmaller than the reference value, said time-delay means including meansresponsive to both said signals for starting said time-delay means, saidtime-delay means including means to stop the operation of the motorafter a' predetermined period if said signal, dependent upon saiddifference between said magnitudes, persists for said predeterminedperiod.

2. Automatic control means for an arc furnace, comprising means formeasuring a variable magnitude of the furnace, an adjusting motor for atleast one of the elec trodes, control means for said motor, anamplifier, a reference magnitude supply means, means connecting saidreference means and said measuring means to said amplifier, saidamplifier emitting signals depending on the difference between theoutput signals from said reference and said measuring means signalmeans, time-delay means connecting said amplifier with said signal meansand including means to furnish a continuous output signal from saidamplifier when the measured value is greater than the reference valueand means to supply a continuous output signal from said amplifier whenthe measured value is smaller than the reference value, said time-delaymeans including means responsive to both said signals for starting saidtime delay means, said time-delay means including means to operate saidsignal means after a predetermined period if said signal, dependent uponsaid difference between said magnitudes, persists for said predeterminedperiod.

References Cited UNITED STATES PATENTS 2,456,936 12/1948 Frostick 1313 X2,942,045 6/1960 Johnson 13-13 2,942,138 6/1960 Carr et a1 13--13 X3,128,364 4/1964 Wanttaja et al. 31468 X 3,143,587 8/1964 Buehl 13-133,217,205 11/1965 Bennett 13-13 X BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, JR., Assistant Examiner.

